1. Field of the Invention
The present invention relates to an adaptive control system and a method thereof which can be suitably used for a controlled object dynamic characteristic of which will be significantly changed.
2. Description of the Related Art
Conventionally, as an adaptive control method used for a controlled object such as a chemical plant dynamic characteristic of which will be changed with time, the following two control methods are known: (1) an adaptive control method which initializes the error covariance matrix at a proper time interval according to the on-line identifying method using as the initial value a system parameter of the controlled object which is identified on the off-line basis, or estimates the system parameter of the controlled object by means of an oblivion coefficient and then determines an optimum feedback gain according to the Ricatti equation by using the estimated parameter, and (2) an adaptive control method which directly calculates the sensitivity of the feedback gain given to the controlled object by using input/output data for the controlled object and then sequentially corrects the feedback gain given to the controlled object by means of the calculated sensitivity.
However, in the control method (1), a plurality of systems (normally, linear systems) which can be easily processed are used as models, one of the models which approximately represents the dynamic characteristic of the controlled object is selected, and an optimum feedback gain of the controlled object is determined by means of the selected model. Therefore, it is difficult to effect the adaptive control for the property which causes variation in the dynamic characteristic and which the dynamic characteristic of the controlled object has but each of the inherent models does not have. Further, the oblivion coefficient and the initialization timing for the covariance matrix in the on-line identification do not always reflect variation in the dynamic characteristic of the controlled object with time. As a result, when the control method (1) is applied to the controlled object dynamic characteristic of which significantly varies, a satisfactory control result cannot be obtained. Besides, in the control method (2), since the sensitivity of the state feedback gain can be calculated directly from the input/output data of the controlled object without effecting the system identification and therefore an optimum feedback gain can be sequentially determined by the gradient method, an adaptive control can be effected for the property inherent to the controlled object. However, the control method (2) has a defect that preliminary information concerning the controlled object such as the initial value of the feedback gain and the dimension number of the controlled object is necessary, and it is often required to effect the state estimation for a normal controlled object. That is, it is impossible to effect the control process if the identification is not effected at all. Further, when the dynamic characteristic of the controlled object is significantly changed, there occurs a problem that the follow-up ability in correction of the state feedback gain attained by sequentially calculating the state feedback gain sensitivity by use of the gradient method is low.